Does the recipient have an iOS device capable of receiving "iMessages"? If the recipient does not or the device you are texting is not an Apple device, you will not be able to send because iPads cannot send "SMS" messages.

Does the recipient have an iOS device capable of receiving "iMessages"? If the recipient does not or the device you are texting is not an Apple device, you will not be able to send because iPads cannot send "SMS" messages.